1. Field of the Invention
The present invention relates to an optical lens system, and more particularly to a four-piece optical lens system applicable to electronic products.
2. Description of the Prior Art
With the consumer electronic industry continuously growing, the current market demand for small imaging lens system is also increasing. Especially for the imaging lens application in mobile phone, tablet computer and notebook, optical lens system has almost become mainstream in the market. Nowadays, as all types of electronic products are becoming thinner, lighter and easier to carry, the imaging lens system also needs to be further reduced in size in order to fit in the increasingly miniaturized carrier. Fine pixel and good image quality have become basic requirements for optical lens system. In addition, consumers also demand that more persons or views can be recorded on a photograph, therefore, it is becoming increasingly important whether an optical lens system has a wide-angle of view or not.
In order to miniaturize the lens system and widen the angle of view, the lens elements of the lens system must have a very short combined focal length so as to form an image within a short distance. As the refractive power of the lens elements increases, the aberration correction will become difficult, and the aberration has to be corrected by arranging more lens elements or using aspheric lens elements. Furthermore, the thickness of the lens elements and the air spaces also need to be minimized, which imposes high requirements on the tolerance during manufacturing and assembling process, making the lens system difficult to manufacture.
Conventional arts, such as U.S. Pat. Nos. 7,715,119 and 7,755,853, use glass as the material of the first lens element to provide better aberration, reduce the size of the lens system while improving image quality. However, the manufacturing cost of the glass lens element is high.
The lens systems disclosed in U.S. Pat. Nos. 8,405,919, 8,395,691, 8,358,475 and 8,199,418, without using glass lens elements, are capable of providing better image quality simply by adjusting the refractive powers and positions of the lens elements. However, the FOV (field of view) of all these lens systems is less than 76 degrees, and the proportion of the total length to the half of the maximum image height of the lens system (TL/ImgH) is greater than 1.6. Since the image angle is small and the total length is relatively long, all these four lens systems cannot satisfy with the demand for wide-angle shooting and miniaturization.
The lens systems disclosed in U.S. Pat. Nos. 8,441,745 and 8,432,622 are capable of wide-angle shooting by using a first lens element with a negative refractive power. However, the total length of these two lens systems is too long to fit in the miniaturized electronic products, such as mobile phone, notebook or tablet computer.
The present invention has been made in order to solve the above-mentioned problems.